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Author

Han, Bo

Date of Issue

2016-05-12

School

School of Mechanical and Aerospace Engineering

Abstract

Nowadays, the demand for high efficiency heat dissipation keeps increasing. Research has been carried out to solve this problem, one of such effort is microchannel heat transfer technology. However, microchannel heat transfer method has many defects, including high pressure loss, high cost and complexity of the devices. In this research, an annular microchannel of 0.3 mm is created by inserting an insert with outer diameter of 19.4 mm into a pipe with inner diameter of 20 mm. Since these two macro geometries can be fabricated by conventional manufacturing method, the microchannel created here is much simpler and less costly. In this project, Fish Scale profile insert, Inverted Fish Scale profile insert and Constructal Fin profile insert are introduced to improve the heat transfer coefficient in the microchannel system, aiming to achieve good heat transfer performance with low pressure drop.
In this project, experiment is conducted to investigate the effect of the profile height (e) variation on the thermal performance, hydrodynamic performance and thermo-hydraulic performance. Keeping channel gap size (H) and pitch length to scale height (P/e) constant, only one geometrical variable is presented for the insert surface profile design, which is scale height to channel height (e/H). The experiment is conducted under the flow rate from 0.5 L/min to 7 L/min and Reynolds number in the range of 300 to 4600. For flow rate 0.5 L/min to 1.75 L/min, the heat rate is 250 W; for flow rate from 2.0 L/min to 7.0 L/min, the heat rate is 1000 W.
Results show that the increment of the profile height (e) has a positive effect on the heat transfer coefficient. For Fish Scale profile insert, the highest heat transfer coefficient value is 47.9 kW/m^2∙K, when the flow rate is 7.0 L/min and the height e=0.21 mm, on the other hand, the highest heat transfer coefficient value is 52.8 kW/m^2∙K, occured at the flow rate of 6.50 L/min when the profile height e=0.21 mm for Inverted Fish Scale profile insert. For profile insert designed through Constructal Fin theory, the highest heat transfer coefficient value is 37.9 kW/m^2∙K, when the flow rate 5.0 L/min and the profile height e=0.3 mm.
In order to study the effect of the profile height (e) on the thermo-hydraulic performance, the thermo-hydraulic performance factor (η) is introduced. For Fish Scale profile insert, the highest η value is 1.32, occurred at the flow rate of 2.75 L/min when profile height e=0.21 mm while the highest η value is 1.43, achieved at the flow rate of 2.50 L/min and at the profile height e=0.21 mm for Inverted Fish Scale profile insert. For Constructal Fin profile insert, the highest η value is 1.35, achieved at flow rate of 2.00 L/min when the profile height e=0.3 mm.
Therefore, the research proves that when the channel gap size and pitch length to scale height is kept constant, increasing the profile height (e) enhances the flow thermal performance and thermo-hydraulic performance in microchannel.